High voltage switching apparatus



Aug. 3, 1965 E. L. LUEHRING ETAL 3,198,986

men VOLTAGE swncnxue APPARATUS Filed July 12, 1962 1 (26 127 i I I i 33CG 3?) CG 33 CG Q4 Q3 Q2 GI 04 Q3 Q2 Ql Q4 Q3 Q2 0! ".35 2| 1: 1; 221:12-23 24/CZ'I DA B J FIG-3 H INVENTORS ELMER L. LUEHRING JOSEPH D.HOFFMAN ATTORNEY United States Patent 0 HllGlll VULTAGE fiWlTCHlNGAPPARATUS Elmer L. Luehring, Cleveland Heights, and Joseph D.

l-lofirnan, Shaker lileights, Ohio, assignors to .loslyn and Supply(30., a corporation of Illinois, High- Voltage Equipment CompanyDivision, Cleveland, Ohio Filed .luly 112, i962, Ser. No. 209,339 7Claims. (ail. 31711) The present invention relates to high voltageswitches and is known to have particular significance in connection withmechanically tandem operation of electrically series connected switchescapable of interrupting alternating current at a point other than atnormal current zero.

While only a single phase operation is described and only single phaseschematics are shown for simplicity, in a complete installation thearrangement may be multiplied to provide for plural phases.

Alternating current interrupters that have natural arc instabilitiestypically do not extinguish at normal current zeros in alternatingcurrent systems. The stability of an arc in such a device is dependentupon many things including: work function of cathode electrode material;vapor pressure of cathode electrode; melting point of cathode electrode;rate of rise of recovery voltage by which is meant the voltage trying toreestablish the arcing condition after extinction; instantaneousdistance of contact separation; maintenance of constant direction ofelectron fiow during arc extinction; temperature of cathode electrode;relative value of system current, etc. While it is true that during theperiod of time that current is increasing an interrupter might notdisplay such instability as a consequence of contact (electrode)separation increasing more slowly than the system current, even so noexception is evident with low maximum value of current, because of therelatively low rate of rise of current where there is such a lowmaximum.

Heretofore for some applications the problem of voltage exceeding thewithstand ability of individual interrupter switches has not been solvedby using series connected interrupter contact pairs. The interruptersare naturally unstable and can be used in series only if the product ofsystem surge impedance (ohms) and electrode maximum instantaneous arcinstability (amperes) is less than the voltage withstand ability of asingle pair of interrupter electrodes when the voltage functions ofthese two quantities are compared instant by instant and added to steadystate system recovery voltages. Thus the usefulness of interrupters hasbeen limited to switching at system voltages where the transientrecovery voltage does not exceed the recovery ability of a single pairof contact electrodes.

Stated in another way, enclosed against ambient switches (such as vacuumswitches) can be connected electrically in series and mechanicallysynchronized as far as possible but even if all could be operated tohave the same contact separation at the same instant (which i not thecase) even so they would not all approach arc instability together. Onewould have its arc go out first, and this would induce a high voltageacross the high impedance of the inherent capacity of that particularswitch, hence raising the withstand voltage rating required of thatparticular switch (and of all the switches for that matter since thereis usually no way of knowing which one will reach arc instabilityfirst).

It is an object of the present invention to provide simple andinexpensive means for overcoming the above mentioned difiiculties.

Another object of the present invention is to provide more economicalswitching, as regards first cost and maintenance factors.

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Broadly stated, in accordance with one aspect of the invention each ofone or more naturally unstable switches is shunted by a circuitcomprising resistance and a number of small air gaps in series. The gapshave normally poor voltage distribution but, because they are arrangedin series, self induction causes a cascading are to elongate and therecovery ability of these gaps is achieved by the improvement of voltagedistribution in the gap system as a result of the presence of arcproducts between the gaps after extinction at a normal system currentZero.

Other objects and various advantages will become apparent and theinvention may be better understood from consideration of the followingdescription taken in connection with the accompanying drawing, in whch:

FIG. 1 is a simplified schematic diagram showing the invention appliedto series connected interrupter switches;

FIG. 2 is a graph showing voltage and current relationships duringoperation of apparatus such as that shown in FIG. 1;

FIG. 3 shows a modification.

For any interrupter switch, as Well as for any arrangement of seriesconnected interrupters, the limit imposed by the single set, or seriessets, of contact electrodes is real because (1) the arc instabilitycharacteristic of any set of electrodes i a statistical variable, and(2) the impedance of an interrupter is highest following a naturalinstability extinction as opposed to an outside influence causng currentreduction or elimination.

It is dilllcult, and probably impossible, to eliminate arc instabilityby choice of electrode materials. Any solution of the problem tated isfurther complicated because any statistically based insurance must bealmost instantaneously compensatory. In some applications, the problemcan be solved by reducing the surge impedance of t e load to bedisconnected, but with many other applications it is not economical tohandle the problem in this manner and it i for such applications thatthe presently described arrangements are useful.

Referring now to FIG. 1, a high voltage source 10 is shown supplying ashunt reactor 11 through a plurality of switches, B3431, connected inseries electrically and mechanically connected to operate substantiallytogether as indicated by the broken lines 12. As described in US. Patent2,955,181, there may be a driver-actuator switch DA for taking into andout of the circuit the plurality of series connected switches which maybe enclosed against ambient, being, for example, vacuum switches, andthought of as bottles. As disclosed and claimed in the above mentionedpatent, arrangements can be made so that, during opening, the bottlecontacts open first, and then the driver-actuator DA opens, so as tokeep the bottle contacts out of the circuit during a later closingsequence through other switches not shown in the present case drawingsbut fully illustrated and described in the above mentioned patent.

As shown in dashed lines in FIG. 1, there are inherent capacitances21-24 from the switch contacts to ground, and inherent capacitances252'7 around the contact pairs of the respective switches. These arestray capacitances dependent in large measure on the dimensions of theswitch contacts and other parts of associate potential and each of themhas one value when the associate switch contacts are closed and a quitedifferent value when the contacts are open. There is some leakageresistance as well, but this need not be considered in connection withthe explanation of the present invention.

When the present invention is applied to more than one interrupterswitch in series, it is essential that something more than the inherentstray capacitances (shown in dashed lines) he provided in order toproperly divide the voltage drop across the respective switch contactpairs. To overcome this there is shown in FIG. 1 for each switch (Bl-B3)a shunt circuit of a series connected resistance 31 and capacitance 32.This divides the voltage more evenly than would the inherentcapacitances particularly when, as is often the case, one interrupter isphysically closer to ground than the others (for example, see thearrangement in the above mentioned Patent 2,955,181

Suppose Bl-BS all start to open together drawing three arcs one of whichwizl almost certainly go .out first and allow the induction of a highvoltage across the high impedance of the inherent distributed capacity(25, 26 or 27), as modified by one pair of 31-32, of that particularswitch. Then the switch has to withstand more voltage after havingbroken the arc than, with or Without the voltage dividing function of31432, it had to stand before it broke the arc. In order to overcomethis I provide a gap system that will break down electrically before theinterrupter switch is damaged by over-voltage and then will interruptthe current flowing through it more nearly at a normal current zero.This can be a system that can withstand more voltage after havingcontained an arc than it could before it contained the arc. The gapsystem is put in shunt across each swivel and, in FIG. 1, each such gapsystem comprises a plurality of series connected quench gaps Ql-Q t, aphysically relatively remote therefrom series calibrating gap CG and aseries resistor 33. Use of the calibrating gap is not essential, as willlater become apparent in the discussion in connection with FIG. 2, butif it is used its gap is sufiiciently small so that as soon as one setof interrupter contacts (Bil, B2, or B3) has its arc reach instabilityand sufficient voltage develops across the contacts, the associatecalibrating gap CG will spark over, and, if the calibrating gap is used,the quench gaps are even smaller, at least as to the space apart of theelectrodes of each, and in series with each gap system there is includeda current limiting impedence. This might be a capacitor but use of apure resistance (33) is advantageous economically. Since the arcinstability is evident below a certain instantaneous value of current,the value of each resistance 33 to be used can be determined by theformula:

where R=value of resistance to be used,

E =peak withstand voltage of the unstable interrupter contact system,and

I =maximum instantaneous current instability level of the unstableinterrupter, as determined by test.

Obviously, then, the gap system breakdown voltage must be less than Ebut as many units of this series parallel system (of interrupterswitches with shunted circuit of resistance and multi-gaps in series)can be placed in series as required to accommodate insulationrequirements so long as the voltage distribution of the units isequalized (as by the resistance capacitor shunts).

The quench gaps, in any event, are suh'iciently small so that as theassociate interrupter contact pair has its arc reach instability, thequench gaps will sequentially spark over shifting current to a newsinusoidal phase representing load plus the particular series resistance33.

This may be more clear from consideration of FIG. 2 where V indicatesthe wave shape of terminal voltage at the source 10. Assuming DA and133-331 in FIG. 1 all closed, 1 represents a first value of currentassumed 90 lagging because of the inductive load 11. Bl-B3 start to opendrawing arcs and as the first one of these arcs is extinguished at atime t the associate one of the resistances 33 completing a circuitthrough all of the associate spark gaps shifts the phase of the currentto nearer unity power factor as indicated at 1 At a time 1 a sec- 0ndinterrupter switch arc is interrupted shifting current to an even morein-phase (and lower amplitude) wave I at i the third interrupter arcgoes outshifting the current to 1 (which is almost the in-phasecondition desired) and ultimately arcing stops across the spark gaps andthe current goes to zero so far as the quench gaps are concerned.Although there may be an infinitesimally small continued current throughthe series circuits of resistances 31 and capacitors 32 this is readilyinterrupted by the switch DA when it later opens.

The use of two or more like dimensioned gaps in shunt across eachrelevant pair of interrupter contacts aids in establishing the propercharacteristics having in mind that not only must any included spark gapspark over on a certain voltage but must, at other times duringoperation, be able to withstand some other voltage value withoutsparking over. As has been known heretofore, ten gaps of 1" thoughconnected in series do not operate the same as one gap of 10'. Becauseof charging currents in the line and hardware one will spark over beforethe others even though the total stack voltage is less than ten timesthe spark over voltage of any individual gap. Thereafter the voltageacross every other gap in the series circuit increases and the effectcascades until all have broken down.

Whether or not a calibrating gap is included in the circuit, inaccordance with the invention there are at least two (and preferablythree or more, and for a single interrupter we have with good resultsused as many in series as forty) quench gaps by which is means pluralgaps having substantially the same dimensions. Thus two or more gapstake the place of one according to the invention and this enables gapspark over at a voltage which is low enough so that it will not damagethe interrupter switch contacts while on transient recovery, afterultimate eX- tinguishment of the are at all sprak gaps, none of thespark gaps will spark over for though there will be higher instantaneoustotal voltage it is more evenly distributed (1) over the gap systems ifthere are more than one, and (2) over the gaps of each system.

There is thus provided an arrangement of the class described capable ofmeeting the objects above set forth. Each system of plural gaps canwithstand more voltage after having contained an arc than before itcontained the arc. Such a system has natural arc stability, and a lowrate of rise of dielectric strength. As many units of this seriesparallel system (of interrupter contacts shunted by series circuit ofresistance and plural gaps) can be placed in series as required toaccommodate insulation requirements providing only that if there is morethan one interrupter switch, the voltage distribution of the units isequalized to coordinate with the requirements (as by use of shunt pathsof resistance 31 and capacitance 32).

FIG. 3 shows another way of taking advantage of the present inventioncomprising small substantially identical gaps in series. Here there isno calibrating gap but there are plural quench gaps Q in series withresistance 33 with this series circuit in shunt with a singleinterrupter contact B. During operation, as B opens self inductioncauses a cascading arc to elongate across the quench gaps and as the gaparc is extinguished there is an improvement of voltage distribution ingap system resuiting from are products which prevents re-establishmentof the are after a normal current zero.

With arrangements according to the invention voltage and current canmore readily reach zero together and in such manner as to minimize thetransient recovery voltage. Less expensive equipment can be used thanheretofore and there is no longer the possibility of subjecting parts totwo times peak voltage but suddenly attempting to open a circuit to aninductive reactance load.

While I have illustrated and described particular embodiments, variousmodifications may obviously be made without departing from the truespirit and scope of the invention which is intended to be defined onlyby the appended claims taken with all reasonable equivalents.

We claim:

1. For use with high voltage switching equipment comprising a pluralityof n vacuum interrupter units electrically in series with one anotherand mechanically connected to operate substantially together,

a plurality of n deliberately provided circuits each comprising a pathin shunt around a dilferent one of said interrupters for substantiallydividing voltage equally over the interrupters,

and an additional plurality of n circuits each comprising a path inshunt around a diflierent one of said interrupters with said lastmentioned paths each comprising the series circuit of a current limitingmeans and a plurality of at least two quench gaps.

2. The combination of claim 1 further characterized by the currentlimiting means in the second mentioned plural circuits comprisingresistors.

3. The combination of claim 1 further characterized by the secondmentioned plural circuits each having at least three quench gaps inseries.

4. The combination of claim 1 further characterized by the secondmentioned plural circuits each having at least three quench gaps and onegap of larger dimension than each of said qunch gaps, all in series withthe current limiting means of the particular second mentioned pluralcircuit.

5. In a circuit a first interrupter means and in shunt therewith theseries circuit combination of a second interrupter means and aresistance whose value is not more than R=WI when E peak withstandvoltage of said first interrupter means and I=maximum instantaneouscurrent instability level of said first interrupter means as determinedby test.

6. Plural series connected circuits each being the circuit of claim 5.

. 7. Plural series connected circuits as in claim 6 furthercharacterized by each first interrupter means comprising contactsoperating in a vacuum.

References Cited by the Examiner FOREIGN PATENTS 27,138 7/16 Norway.588,204 11/33 Germany.

SAMUEL BERNSTEIN, Primary Examiner.

1. FOR USE WITH HIGH VOLTAGE SWITCHING EQUIPMENT COMPRISING A PLURALITYOF "N" VACUUM INTERRUPTER UNITS ELECTRICALLY IN SERIES WITH ONE ANOTHERAND MECHANICALLY CONNECTED TO OPERATE SUBSTANTIALLY TOGETHER, APLURALITY OF "N" DELIBERATELY PROVIDED CIRCUITS EACH COMPRISING A PATHIN SHUNT AROUND A DIFFERENT ONE OF SAID INTERRUPTERS FOR SUBSTANTIALLYDIVIDING VOLTAGE EQUALLY OVER THE INTERRUPTERS, AND AN ADDITIONALPLURALITY OF "N" CIRCUITS EACH COMPRISING A PATH IN SHUNT AROUND ADIFFERENT ONE OF SAID INTERRUPTERS WITH SAID LAST MENTIONED PATHS EACHCOMPRISING THE SERIES CIRCUIT OF A CURRENT LIMITING MEANS AND APLURALITY OF AT LEAST TWO QUENCH GAPS.